This invention relates to piezoelectric ignition devices, and, more particularly, to an insulator assembly for an electric conductor of a piezoelectric ignition device.
Piezoelectric ignition devices are commonly used for igniting propane lanterns, barbecue grills, etc. A piezoelectric ignition device generally includes a piezoelectric crystal, an impact hammer for striking the crystal, and an electrode for conducting voltage from the crystal to the point of ignition. The outer and of the electrode is spaced from a grounded conductor. The piezoelectric crystal generates a voltage when it is impacted by the hammer, and propane or other fuel is ignited when the piezoelectric electrode arcs to ground.
The electrode for the piezoelectric crystal must be insulated from adjacent grounded metal other than the ground at the point of ignition. The ignition device is subjected to severe mechanical shock loads each time the device is activated, and the insulator is also subjected to mechanical shock loads by the impact hammer. The insulator should therefore be capable of withstanding continual shocks over a long period of time. Since the insulator is located near a flame, the insulator should be flame-resistant. Many piezoelectric ignition devices are used outdoors, and the insulator must be able to withstand 100% moisture and severe cold.
One type of insulator which has been used is a molded insulator tube of dielectric refractory material such as ceramic. The insulator tube surrounds the conductor and insulates it from adjacent metal. However, such refractory tubes are brittle and are subject to cracking under repeated mechanical shocks. Shocks can be transmitted directly from the crystal to the insulator, or radial shocks can be transmitted to the insulator by the electrode. Once the insulator tube cracks, the conductor can arc to ground through the crack.
Another insulator which has been used is a Teflon sleeve which surrounds the insulator. However, a Teflon sleeve will melt under direct flame or near-flame conditions.
One type of prior art lantern isolates the insulator and the electrode from shock by mounting the piezoelectric crystal remotely from the flame and connecting the electrode to the crystal with a wire lead. This assembly is very expensive to install.
U.S. Pat. No. 4,051,396 describes a piezoelectric device in which the piezoelectric crystal is surrounded by an insulating bushing, and the crystal and the bushing are encapsulated with an insulating viscous fluid such as epoxy resin without hardener.